At least 2,000 police officers were subject to three or more complaints by members of the public in the last year, figures obtained by the BBC have shown.
The statistics from 43 out of 52 UK forces show more than 5,000 complaints made against officers in 2009-10.
The forces with the most multiple complaints per officer were in Northern Ireland, West Mercia and Lincolnshire.
The Police Federation, which represents 140,000 officers in England and Wales, said many cases were unsubstantiated.
Failure of duty
The figures obtained from a Freedom of Information request by the BBC show 2,073 officers had three or more complaints against them, and there were a total of 5,069 allegations against officers.
Most complaints were about rudeness, assault or failure of duty.
The force with the most officers with three or more allegations against them, regardless of the size of the force, was the Police Service of Northern Ireland with 376.
The London's Metropolitan Police was second with 273 officers, from a total of 1,719 allegations, followed by Greater Manchester with 160, Kent with 130 and West Mercia with 117.
In Dyfed-Powys, 40 allegations were made against one inspector and 38 against one constable during the year.
Only a minority of forces gave the BBC details about the outcomes of allegations, but of these more than half led to no further action.
In Greater Manchester there were 866 allegations for the year, of which 562 led no further action, action was taken in one case, and 303 are still ongoing.
One officer in the West Midlands had to wear a headcam while on duty as a result of allegations made, and another had their Taser training deferred.
In the Met, one officer had 10 allegations of "lack of fairness and impartiality" and another 10 of "other neglect or failure of duty" brought against him but these were logged as a single complaint.
The Met did not provide any information on the outcome of these complaints, saying the figures were not available.
In July, Northern Ireland's Police Ombudsman Al Hutchinson said the number of complaints about police officers' conduct was at its highest level in eight years.
The 3,500 allegations were an increase of 14% on the previous year.
BBC home affairs correspondent Danny Shaw said most constabularies operate a system which identifies officers who have been the subject of more than one complaint in case there is an underlying problem in relation to a particular officer.
The Police Federation said its members did a difficult job in difficult circumstances.
Rob Garnham, the chairman of the Association of Police Authorities (APA), which represents police organisations in England, Wales and Northern Ireland, said any complaints against the police had to be treated seriously and fairly.
He said: "As part of the government's planned reforms to policing, the APA will be proposing that the independence of the complaints process is strengthened so that it is more transparent and accountable to the public.
He added: "Police authorities are committed to ensuring that the public has full confidence that every complaint will be taken seriously, and upheld where appropriate, particularly where the complaints involve the same police officer."